Mouth, pharynx and esophagus

The nasopharynx lies behind the nasal cavity, above the soft palate, which lifts to seal it during a swallow. The oropharynx and laryngopharynx carry both air and food.

• The oropharynx:
• The laryngopharynx:
• Correct: The nasopharynx:

Exocrine glands release their products onto an epithelial surface or into a lumen, usually through ducts. Endocrine glands release hormones into the blood.

• It secretes into the blood with no duct:
• Correct: It secretes onto a surface or into a cavity, usually through a duct:
• It is made of nervous tissue:

The inner circular and outer longitudinal layers of the muscularis externa produce peristalsis.

• Correct: The muscularis externa:
• The submucosa:
• The serosa:

The lower esophageal sphincter is the zone at the junction of the esophagus and the stomach, just below the diaphragm.

• Upper esophageal sphincter: The upper esophageal sphincter is at the top of the esophagus, where it meets the pharynx.
• Correct: Lower esophageal sphincter: Correct. It guards the junction with the stomach.
• Diaphragm: The diaphragm is the sheet of muscle the esophagus passes through; it helps the sphincter but is not the pinned structure.
• Trachea: The trachea lies in front of the esophagus in the neck and upper chest, not at the stomach.

The pharyngeal phase is the reflex that seals the airway: vocal fold closure, elevation of the larynx and tipping of the epiglottis, timed by the swallowing center in the medulla and pons. The patient can still start a swallow voluntarily, but the reflex that should protect the airway is slow or weak, so liquid enters the larynx.

• The voluntary phase, started by the cerebral cortex and the tongue: He can chew and push food back, so the voluntary phase works.
• Correct: The pharyngeal phase, run by the brainstem swallowing center: Correct. Airway protection is part of the pharyngeal phase, and its center is in the damaged brainstem.
• The esophageal phase, carried out by peristalsis in the esophagus: The esophageal phase starts only after the bolus has passed the pharynx. Liquid entering the larynx means the failure is earlier.
• Secretion of saliva by the glands that lubricate the bolus: Thin liquids need no lubrication. Their danger is that they move fast and reach the larynx before a weak reflex closes it.

Breathing stops for about a second during the pharyngeal phase. The airway is closed, so air cannot move, and a breath in at that moment would pull food into the larynx.

• The soft palate and uvula lift and seal the nasopharynx: This step is right. The soft palate lifts and keeps food out of the nose.
• The vocal folds close: This step is right. Closing the vocal folds seals the airway from inside, at the very start of the swallow.
• The larynx is pulled up and forward, and the epiglottis tips over its opening: This step is right. The larynx tucks under the tongue and the epiglottis covers it.
• Correct: Breathing speeds up to keep oxygen flowing during the swallow: This is the error. Breathing pauses during the pharyngeal phase.
• The pharyngeal constrictors squeeze the bolus down into the esophagus: This step is right. The constrictors contract from top to bottom as the upper esophageal sphincter opens.

Atropine removes the parasympathetic drive to the salivary glands, so the mouth becomes dry. Less saliva means less amylase, a stickier bolus that is harder to swallow, and weaker taste.

• Volume of saliva: down. Parasympathetic fibers drive the large, watery flow of saliva through muscarinic receptor proteins, and atropine blocks them.
• Starch digestion in the mouth: down. Less saliva means less salivary amylase mixed with the food.
• Ease of swallowing dry food: down. With little saliva and mucus, chewed food does not bind into a slippery bolus.
• Ability to taste a dry cracker: down. Taste molecules must dissolve in saliva to reach the taste buds.

Lysozyme damages bacterial walls, IgA binds microbes on mucous membranes, bicarbonate buffers acids made by mouth bacteria, and mucus coats and protects the lining. Amylase digests starch, and bile is not in saliva.

• Correct: Lysozyme: Correct. Lysozyme attacks bacteria.
• Correct: IgA antibodies: Correct. IgA is the antibody class secreted onto mucous membranes.
• Correct: Bicarbonate: Correct. Bicarbonate buffers acid that would dissolve enamel.
• Salivary amylase: Salivary amylase digests starch; it is not a defense.
• Correct: Mucus: Correct. Mucus coats the lining and traps microbes.
• Bile: Bile is made by the liver and enters the small intestine. It is not part of saliva.

This is heartburn from reflux. Lying down after a large meal lets acid flow back past the lower esophageal sphincter into the esophagus, whose squamous lining has few defenses against it. Frequent reflux like this is GERD.

• Reduced blood flow to the heart muscle through narrowed coronary arteries: Heart pain is usually brought on by exertion and is not relieved by antacids. Chest pain always needs heart causes ruled out, but this pattern fits reflux.
• Correct: Stomach contents flowing back past the lower esophageal sphincter: Correct. Timing with meals and lying down, and relief with antacids, point to acid reflux.
• A piece of food stuck at the upper esophageal sphincter: Food stuck at the top of the esophagus causes trouble swallowing and a feeling of something in the throat, not nightly burning after meals.
• Inflammation and swelling of both parotid glands: Parotid inflammation causes swelling in front of the ears, not pain behind the sternum.

The esophagus is lined by nonkeratinized stratified squamous epithelium, built for abrasion, not acid. The stomach's lining has its own defenses against acid, which the stomach topic explains. Where the two linings meet, the change is abrupt.

• The esophagus has a thicker muscle layer that the acid can reach more easily: Acid damages the lining first; muscle thickness has nothing to do with why the lining is vulnerable.
• Correct: Its stratified squamous lining lacks the stomach lining's acid defenses: Correct. The squamous lining lacks the acid defenses of the stomach's lining.
• The esophagus has a serosa that absorbs acid: In the chest the esophagus has an adventitia, not a serosa, and neither layer absorbs acid.
• Acid is stronger in the esophagus than in the stomach: The acid comes from the stomach, so it is diluted, not concentrated, when it refluxes.